1. Field of the Invention
The present invention relates to a process for suppressing the precipitation of sediment in the unconverted residuum from a virgin residuum conversion process. This invention is also directed to a composition of matter comprising a virgin residuum with high asphaltene content and an unconverted residuum from a conversion process.
2. Description of Related Patents
Petroleum crude oil is generally separated into constituent fractions having separate boiling points by atmospheric distillation at temperatures of about 675.degree.--725.degree. F. (357.degree.-385.degree. C.) so as to obtain distillate products such as gasoline, with a heavy residue remaining as bottoms product, commonly referred to as virgin residuum. The virgin residuum, in turn, may be subjected to further treatment, e.g., a thermal cracking operation commonly known as visbreaking or a catalytic conversion process such as hydrocracking or cat cracking, to obtain additional converted distillate products from the crude oil. The thermally cracked residual components contained in the unconverted residuum remaining from the cracked operation tend to be incompatible with other distillate or residual components and to precipitate asphaltenes as sediment when blended therewith.
Such precipitation has traditionally been prevented by limiting the amount of conversion in the visbreaker, thereby reducing yields of desirable product. An alternative method is to add highly aromatic flux stocks, which are highly cracked stocks without asphaltenes, to the unconverted residuum, as, for example, taught by U.S. Pat. No. 2,360,272, which uses, e.g., the heavy fraction from catalytic hydroforming or the heavy cycle oil from cat cracking.
U.S. Pat. No. 2,755,229 describes a method of stabilizing visbroken residuum of petroleum crudes by adding any virgin residuum thereto, with the minimum total volume of virgin stock and cutter oil added being approximately equal to the volume of unstable vibroken fuel oil.